Improved screw-propeller



UNITED STATES JOHN E. ROOT, OE

NEW YORK, n. Y.

IMPROVED SCREW- PROPELLER.

Specification forming part of Letters Patent No. 47,864, dated May 23,1865.

.To all whom it may concern:

Be it known that I, JOHN B. ROOT, of the city, county, and State of NewYork, have invented a new and useful Improvement in Screw-Propellers;and IV do hereby declare that the following is a full, clear, and exactdescription of the same, reference being had to the accompanyingdrawings, forming part of this specification, in which- Figure l is aface view of a propeller constructed according to my invention. Fig. 2is a similar view of the wooden pattern from which a propeller is cast,illustrating the form and construction of the-blades. Fig. 3 is an axialsection in the plane indicated by the line d d in Fig. 2. Fig. 4 is atransverse section of one of the blades in the plane indicated by theline a a. in Fig. 2. Fig. 5 is a transverse section of one of the bladesin the pla-ne indicated by the line b b in Fig. 2. Fig, 6 is a face viewillustrating al modification of the blades. Fig. 7 is a transversesection of one of the blades in the plane indicated by the line c c inFig. 6.

Similar letters of reference indicate corre' spending parts .in theseveral gures.

This invention relates to the construction of the operating-faces ofscrew -propeller blades with a hollow curvature, both in the directionof their revolution and in the direction in which the propelling forceis required to be exerted, the effect of such curvature being to makethe propeller collect the water from its periphery and draw it towardits axis and to discharge or deliver it in a compact column in adirection parallelwith its axis, thereby preventing the formation of avacuum in front of it and effecting the delivery of the whole ofthewater acted upon or set in motion by it in a direction to produce thebest of the Water toward the axis of the wheel, and to prevent theeddyin g of the water in rear of the said hub and allow it to pass offfreely the rear portion of the hub is made of conical form; andmyinvention consists, secondly, in a novel and very convenientconstruction of and mode of tting and attaching the conical rear portionofthe hub.

To facilitate the explanation of the manner in which the pitch of theblades A A is diminished from the periphery toward the axis, one of theblades is represented in Figs. 2 and 3 divided in planes perpendicularto its axisinto a series of laminae, e cl c3 c4 ei e6 e7 6*. The

.curvature of these laminas is in a forward direction-that is to say, inthe direction in which the propeller rotates, which is `-indicated by anarrow in those figures and the said curvature-represented as of arc formand these arcs are described from points or centers in a number ofequidistant radial lines, as shown in Fig. 2, the center from which theiirst one e', is struck being on the rst radial line and farther fromthe axis of the propeller than any of the others, t-hatfrom which thenext one is struck being on the next radialline and nearer to the axisof the propeller; that from which the third is struck being on the thirdradial line and still nearer to the axis, and so on. By thisconstruction the pitch of the inner portion ofthe blade is extended overa' larger portion of the circumference ot' the hub and its degreediminished. This circumferential extension of the inner portion of theblade is illustrated in Fig. 2. The diminution of the 'pitch toward thecenter and the hollow curvature across the face of the blade, or in thedirection in which the propelling force is to be exerted, areillustrated in Figs. 4 and 5, by a comparison of which it will be seenthat the angle formed by the blade with the axis.I of t-he propeller isscarcely greater in the line a a than it is in the line b b, which is attwice the distance from the axis. In making the wooden pattern for theblades, the said pattern is first made of laminze, as described,andfinished by removing the edgesof the said laminte, and thereby makingsmooth surfaces.

It is not desirable to continue the diminution of the pitch all the wayto the hub B, for the reason that it would bring the portion of theblades next the hub, where but little propulsive eifect is obtained, toonear perpendicular to the axis of the propeller, and cause them to dragin the Water. This may be obviated by making the inner portion of theblade, or the portion next the hub, tangential to the curves, by whichmeans the said portion is prevented from being extended so far in acircumferential. direction, as will be seen by a comparison of Fig. 6with 2. Fig.

C is the` conical extension ofthe rear of the hub, by which theformation of a drag in rear of the hub is prevented, and the freedelivery of the water drawn in toward the axis of the propeller isprovided for. This extension is composed of arhollow cone or conicalcasting.

The edges of the base of the cone are fitted into a groove, i, in therear of' the hub, as shown in Fig. 3, and the casting is secured inplace by means of a bolt, f, screwed into the end of' thepropeller-shaft D, and a nut, g, screwed on to a screw-thread on therear of the said bolt outside of the cone. By making the hub hollow andapplying a Water-tight packing in the groove i at the junction of theconical casting with it, the hub and cone are caused to give buoyancy tothe propeller and relieve the shaft in some degree of' its weight.

I am aware that screw-propellers with a pitch varying or expanding ir. adirection lengthwise of the axis are old. I do not, however, vary thepitch in the same direction, but diminish it from the periphery towardthe axis. I am also aware that screw-propellers have been made with acurvature forward or in the direction of the revolution, but I onlydesire to use this forward curvaturein combination with such adiminishing pitch as I have described, the object being to make apropeller Which has a powerful concentrating action upon the water, andat the same timeto obtain a beneficial eifect from such concentratingaction. 1n other propellers-such, for instance, as Nystroms-with theblades curved as above described, when the curvature is suoli as toobtain a powerful concentration ofthe water, areaction takes placein thecenter of` the propeller, which causes the water, or a portion of it, torush out of the propeller along the hub in a forward direction, insteadof all passing out ina rearward direction, as it should to produce themaximum propulsive effect upon the vessel. The cause of such reaction inconcentratin g propellers is that the pitch or surface of the blade asit approaches the center becomes too nearly parallel With the axis of'the propeller, consequently has not sufficient Obliquity of action, asregard the axis of the wheel upon the water, to discharge the largeamount of water that is concentrated upon that portion of the blade in arearward direction, and a portion of the water seeks an outletin aforward direction. By diminishing the pitch of the blade as itapproaches the center the distance which that portion of the blade wouldscrew through the water at one revolution of the wheel is alsodiminished or that portion of the blade acquires a tendency to drag, as'the outer portion of' the blade having the greatest pitch is inclined totravel the fastest in the direction of the axis of the wheel. Now, thisdragging or backward action of the inner portion of the blade bydiminishing pitch seems to have been avoided heretofore in all wheelswith which I am familiar, and it undoubtedly shouldbe avoided in wheelswith straight or nearly straight blades; but in curved or concentratingblades it becomes necessary, in order that the blade may have sufficientObliquity of action toward the center and when the greatest amount ofwater is concentrated upon it, to discharge it all in a rearwarddirection and with a force more directly in line with the axis of thewheel. I contend that the drag or back action which occurs against theinner portion of the forward surface of the blade, owing to thediminished pitch toward thecenter of the propeller, does not operateinjuriously, for the reason that the gain by the more direct action ofthat portion of the blade nearer the center upon which a great quantityof water is concentrated and discharged astern is greater than the lossb v the drag against the forwardsurface of the blade caused by thediminished pitch toward the center, for the drag or back action againstthe forward surface of the blade has a tendency to turn the wheel in therequired direction, thus giving back to the wheel nearly all the powerthat is lost by the drag. The dragging action ofthe blade upon the wateralso has a tendency to prevent the Water which passes through the wheelfrom acquiring a rotary motion in the direction of the revolution of thewheel, as the water is deflected in an opposite direction by the forwardsurface ofthe blade against which the dragging action takes place fromthat which is discharged from the after surface of the blade by itsaction against the water.

I do not claim the curvature of the blades of a propeller in a forwarddirection nor do I claim, broadly, the conical hub; but

What I do cla-im as my invention, and de sire to secure by LettersPatent, is

l. A screw-propeller, the blades of which have a curvature forward, orin the direction of the revolution, combined with such a hollowcurvature of the faces as is produced by a diminution of the pitch fromthe periphery toward the axis ofthe propeller, substantiall y as hereinspecified.

2. The hollow rearward conical extension O of the hub, attached to bodyB thereof', by being fitted into a groove, z', in the body, and securedby a central bolt, f, which passes through the said extension, and isscrewed into the end of the propeller-shaft, substantially as hereindescribed.

JOHN B. ROOT.

Witnesses:

HENRY T. BROWN, J. W. GooMBs.

